Our present invention relates to a key for a cylinder lock, especially for locking systems and, more particularly, for a cylinder lock of the type in which a cylinder core has a key channel which opens at a cylindrical periphery of the core so that the back of the blade of the key can lie substantially flush with its cylindrical periphery and wherein the key has a profile region which can be formed with longitudinal grooves and recesses formed by drilling, milling or other cutting operations and can form bits in the blade cooperating with tumbler pins of the cylinder lock. The term "locking systems" is used to describe systems of locks in homes, large administration buildings and wherever a multiplicity of locks may be required with selective access, exclusive access submaster-key access, grandmaster-key access, etc.